New F6 Motorway A 'Toll Trap', Says Opposition

A new underground tunnel for motorists travelling near Sydney airport has been dismissed as a "con job" and "toll trap" by the NSW opposition.

The NSW government on Tuesday released plans for the four-kilometre F6 motorway extension, running from the M5 at Arncliffe to President Avenue in Kogarah.

The project is set to cost up to $2.6 billion and will be tolled.

Drivers will pay an estimated $1.77 each way for cars to use the new section, but that rises to around $4.53 when they continue along WestConnex.

"We want to be up-front with the community now and say this is one of those roads which will be tolled, but as always there will be a free alternative," NSW Roads Minister Melinda Pavey said.

Labor leader Luke Foley said residents of the Illawarra and Sutherland Shire had for generations expected an "F6" to mean a motorway taking them all the way from the city to Sydney's southern outskirts.

"What a con," he told reporters on Tuesday.

Mr Foley accused the government of being "addicted to tolls".

"This is simply about making the WestConnex business model stack up."

Ms Pavey denied it was simply a "funnel" into WestConnex, describing it as an important "add-on" to Sydney's road network.

"A network that we're creating, that we're delivering with the support of tolls so we can also spend money on public transport," she told reporters.

The controversial toll road has caused disruptions during construction and required the compulsory acquisition of properties.

The cost of WestConnex was revised to $16.8 billion in late 2015 - some $6.8 billion more than first estimated.

Since then, it's been subject to a series of leaks about potential further cost blowouts, which have been damaging for the coalition government.

"(It) essentially creates a toll trap at President Avenue, Kogarah," he said.

The government says the tunnel will let drivers bypass 23 sets of traffic lights and take more than 10,000 vehicles off the often-clogged General Holmes Drive.

But the NSW Greens say it's a "huge burden" on people and the environment.

"This government is locking Sydney into an ever-tightening noose of motorways, where people will have no escape from paying thousands of dollars in tolls," the party's roads and transport spokeswoman Mehreen Faruqi said in a statement.

Mr Foley wouldn't answer whether he would scrap or alter the F6 plans if he wins the 2019 state election, only saying Labor would reveal its hand "well and truly" before the poll.